Clinical and laboratory studies are conducted to determine etiology (infection, immunity and/or genetics) of chronic diseases of the peripheral and central nervous system. Current studies include amyotrophic lateral sclerosis, (ALS), polymyositis/dermatomyositis, new post-polio muscle weakness, demyelinating polyneuropathies, neuromuscular complications of AIDS, certain metabolic muscle diseases and Duchenne's muscular dystrophies. Combined clinical data, and studies of virus serology and virus isolation are performed. A neuromuscular disease that occurs in patients who have had poliomyelitis at an early age (post-polio syndrome) has been clinically defined along with the rate of progression, the electrophysiological, virological and histochemical findings. The nature of oligoclonal bands found in the CSF of patients with post-polio and other chronic neurological diseases is under investigation. Patients with polymyositis are studied and the muscle changes before and after a randomized double-blind controlled study with cyclophosphamide, plasmapheresis of lymphocytopheresis are investigated. Muscle biopsies from patients with Duchenne's muscular dystrophy are studied biochemically to define abnormal proteins (i.e. nebulin). The clinical, electrophysiological and immunological picture of a chronic, sensory, "ataxic" neuropathy were defined and the presence of a ganglionopathy was found. The role of retroviruses in this neuropathy is under study in view of the finding of such neuropathy in patients with HIV and HTLV-I. The metabolic activity of the cortex in ALS patients was studied using the PET scan and 18FDG; hypometabolism was demonstrated not only in the motor but throughout the cortex, suggesting that ALS is a generalized process affecting many cortical regions. Correlation of these metabolic abnormalities with pathology of the cortical neurons is now attempted. Muscle biopsies from patients with nephropathic cystinosis and renal Fanconi syndrome were studied morphologically and biochemically. Signs of a metabolic lipid storage myopathy due to carnitine deficiency were found which prompted a therapeutic study with carnitine replacement.